In recent years, with the multimediatization of information in cellular mobile communication systems as represented by mobile phones or the like, it is becoming popular to transmit not only audio data, but also a large amount of data such as still pictures, moving pictures and the like. To realize the transmission of such large amounts of data, a technology in which a high-frequency radio band is used to obtain a high-transmission rate is being actively studied.
However, when a high-frequency radio band is used, while a high transmission rate can be expected at a short range, attenuation due to transmission distance becomes greater, the longer the range. Accordingly, when the mobile communication system employing a high-frequency radio band is actually operated, the coverage area of each base station becomes small, which thus requires that a greater number of base stations be set up. Since the set-up of base stations involves large costs, a technology is strongly demanded for realizing communication services which employ a high-frequency radio band, while reducing an increase in the number of base stations.
To address these demands, a technology is investigated in which, a mobile station is used as a relay station, and a communication network formed directly between a base station and a mobile station, and a communication network (ad-hoc network) formed via the relay station are formed, and diversity gain is obtained by combining, at the base station, the received signals of both communication networks (for instance, refer to Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-189971